This invention relates to monitoring a critical value of a parameter and sending the critical value to a system controller.
Sensing devices, such as those in a security system, send messages to a system controller, which then interprets the messages and generates a response. The sensors are typically remote from the system controller and have a separate energy source, such as a battery. Since the energy source of the system controller and remote sensors are separate, the system controller has no information on whether any of the remote sensors have adequate battery power to send messages to the system controller.
Additionally, the energy level varies during operation of the sensor. When the sensors are not generating messages, the energy requirements are minimal. However, the energy requirements increase when generating and sending messages. In a battery-powered sensor, the battery voltage typically decreases during the active period as the sensor is generating and sending messages. The voltage may recover during a following period when no activity is detected by the sensor. In a system where the sensor generates a series of message packets each time the sensor is activated, the battery will typically have its highest voltage when generating the first message packet and the lowest level when generating the last message packet.
The sensor energy level or other important parameter should be transmitted to the system controller at a time when the information is most likely to be successfully communicated to the system controller, i.e., when the battery voltage is highest. Once a low battery condition is detected in a battery-powered sensor, sending the low-battery information in one of the latter packets reduces the likelihood that the system controller will receive and decode the information. The low battery information should be sent at a time when the battery has recovered and is more likely to have sufficient energy to generate a message that is successfully received and decoded by the system controller.